This invention relates to a machine having a rotor which is mounted such that it can rotate about a rotation axis and has an outer rotor housing attached to axial rotor shaft parts and encloses a winding former with a superconducting winding. The rotor also has a device to hold the winding former within the rotor outer housing, which device comprises a rigid connecting device, on a torque-transmitting side, between the winding former and the associated rotor shaft part with at least one torque-transmitting, hollow-cylindrical connecting element composed of plastic reinforced with fiber material. Furthermore, units are provided for cooling and thermal insulation of the superconducting winding. A corresponding machine is disclosed in U.S. Pat. No. 5,880,547.
Electrical machines, in particular generators or motors, generally have a rotating field winding and a stationary stator winding. In this case, the current density and hence the specific power of the machine, that is to say the power per kilogram of its own weight, can be increased, and the efficiency of the machine can also be increased by the use of cryogenic conductors, in particular superconducting conductors.
Cryogenic windings for electrical machines generally have to be thermally insulated from the environment and have to be kept at the necessary low temperature by a coolant. Effective thermal insulation can, in this case, be achieved only if the cryogenic parts of the machine are as far as possible separated from the warm outer area by a hard vacuum with a residual gas pressure of generally less than 10xe2x88x923 mbar, and if connecting parts between these cryogenic parts and the warm outer area transmit as little heat as possible.
Two variants in particular are known for vacuum insulation of rotors with cryogenic rotor windings and warm stator windings: in a first embodiment, the rotor has a warm outer housing and a closed vacuum area which rotates with it. The vacuum area should in this case surround the cryogenic area on all sides (see, for example, xe2x80x9cSiemens Research and Development Reportsxe2x80x9d, Volume 5, 1976, No. 1, pages 10 to 16). However, heat is transmitted in an undesirable manner to the cryogenic parts via supports which extend through the vacuum area. In a second embodiment, the essentially cold rotor rotates in a hard vacuum. In this case, the outer boundary of the hard vacuum area is defined by the inner bore in the stator. However, an arrangement such as this requires shaft seals which are proof against a hard vacuum between the rotor and the stator (see, for example, DE 27 53 461 A).
The machine which is disclosed in the initially cited U.S. patent document uses the first-mentioned embodiment. The superconducting winding of its rotor is located in the interior of a rotor cystostat which, together with flanged shafts that are fitted, forms an outer housing of the rotor. Helium cooling is provided for the superconductors of the winding. In contrast, the outer contour of the rotor outer housing is at approximately room temperature, and even possibly above room temperature during operation. The useful torque from the machine is produced in the rotor winding. The rotor winding is arranged in a cold winding former which is itself suspended or held in an insulated manner in the rotor outer housing, which acts as the cryostat. In this case, this suspension or retention on the drive side of the rotor, which is frequently referred to as the A side of the machine, must be sufficiently robust to transmit the torque from the cold winding former to a shaft part on the drive side. A corresponding rigid connecting device must therefore be designed to be relatively solid in order to transmit torque, and must be connected to the winding former and to the drive-side shaft part such that power can be transmitted. This leads to heat unavoidably being introduced into the cold area of the rotor. The connecting device is therefore frequently cooled separately (see, for example, xe2x80x9cHandbook of Applied Superconductivityxe2x80x9d, Vol. 2: Ed.: B. Seeber, Institute of Physics Publishing, Bristol (GB), 1998, pages 1497 to 1499 and 1522 to 1530).
At the same time, this connecting device also provides the drive-side centering for the cold winding former. On the opposite rotor side, which is also referred to as the non-drive side or in general also as the B side, because important connections for operation of the machine, such as a coolant supply, are provided in it, virtually no torque is emitted. Only the functions of centering and thermal insulation therefore need be provided here. Furthermore, measures must be provided to compensate for the shrinkage of the cooled-down winding former.
In order to reduce the amount of heat introduced into the cooled superconducting area of the rotor, one specific embodiment of the known machine provides for the torque-transmitting connecting device to have, at least on the drive side, a hollow-cylindrical connecting element composed of a glass-fiber-reinforced plastic. This hollow cylinder is provided in each of its two axial ends with a coupling element made of steel, which is connected to the winding former and to the drive shaft such that power can be transmitted. The mechanical connection between the hollow cylinder composed of plastic and the coupling elements composed of steel must ensure a high degree of resistance to overloading and fatigue strength in response to alternating loads since considerably greater torques than during normal operation occur on motors such as these, for example during starting and in the event of various defects, and these must not cause any damage to the connecting device. However, the U.S. patent document contains no details relating to the connection between the hollow cylinder and the coupling elements.
In addition to metallic superconductor materials such as NbTi or Nb3Sn which have been known for a long time and are used in the machines mentioned above, metal-oxide superconductor materials with critical temperatures above 77 K have been known since 1987 as well. Attempts have been made using conductors made of such high-Tc superconductor materials, which are also referred to HTS materials, to produce superconducting windings for machines (see, for example, WO98/02953). Owing to the temperature differences between the operating temperature of the superconductor material and the outside temperature in the warmer rotor outer housing, even machines with this type of conductor require measures to reduce the temperature which is introduced into the superconducting area.
One possible object of the present invention is to specify a suitable connecting device for torque transmission for a machine having the features mentioned initially, which device allows a connection which transmits power and ensures high fatigue strength and a high overload capacity in a relatively simple manner between the cold winding former and the associated warm rotor shaft part, and which in the process limits conductive heat losses to the cold winding former.
The inventors propose a connecting element composed integrally of end-face end parts with a center part located in between them, the end parts should have a corrugated shape seen in the circumferential direction, while the center part should not be corrugated, the connecting element should be connected on the end parts to flange-like end pieces composed of metal such that power can be transmitted when they engage in one another, with
a) the end parts projecting completely and the center part in each case projecting to a certain extent into groove-like recesses in the respective flange-like end piece,
b) at least one side wall of each recess having a corrugated shape which is matched to the corrugated shape of the respective end part,
c) the corrugated shape of each end part resting at least partially on the corrugated shape of the side wall of the corresponding recess, and
d) those parts of the connecting element which are arranged in the recesses being fixed by at least partial filling of the remaining areas of the recesses.
Furthermore, the flange-like end pieces in the machine should be connected in a power-transmitting manner to an associated part of the winding former and/or to a side part, which is connected to the rotor shaft part, of the rotor outer housing.
The advantages associated with this refinement of the machine are that the particular refinement of the hollow-cylindrical connecting element results in good power transmission between the poorly thermally conducting part of the hollow-cylindrical connecting element and the metal parts of the winding former, at least in the area of its end-face end parts. This improvement occurs because of the corresponding configuration of the flange-like end pieces in the connecting area with these end parts. In this case, problems with the shear strength, in particular with respect to overloading and during continuous operation, are advantageously avoided in the connecting area between the plastic and the metal, which otherwise represents a weak point for torque transmission, in that the torque is now primarily transmitted by compression and less by shear in the groove-like cutouts. In order to improve the power transmission, the connecting element may be adhesively bonded to the flange-like end pieces. In this case, the end parts are effectively wedged into the groove-like recesses in the respective flange-like end piece by the filling. This is because the corresponding wedges composed of the filling material, such as a plastic which can be cured, at least largely fill the intermediate spaces between the corrugated end parts and the side walls of the groove-like recesses. A wedging process such as this not only prevents the connecting element from sliding out of the recesses, but also improves the power transmission by compression forces instead of shear forces in the xe2x80x9cmetal-plasticxe2x80x9d connecting area.
Particularly uniform distribution of the forces when torque is being transmitted can be ensured by corrugation on at least one side wall of each cutout and the interlock with the respective correspondingly corrugated end part, seen in the circumferential direction. Since, in addition, the uncorrugated center part (which is in the form of a smooth hollow cylinder) of the connecting element likewise projects to a certain extent into each of the cutouts, where it is fixed and thus connected to the respective metal end piece such that power can be transmitted. This avoids particular loads in the transitional area between the corrugated end part and the uncorrugated center part. The uncorrugated configuration of the center part also advantageously helps to reduce the risk of this part bulging.
It can thus be regarded as advantageous to provide the end parts with a corrugated shape that is distributed uniformly over the circumference. In this case, the corrugated shape may be sinusoidal. Such a refinement of the end parts and hence of at least one side wall of the respectively associated groove-like recess makes it possible to ensure that power is uniformly transmitted between these parts.
It is also particularly advantageous for at least the majority (that is to say more than half) of the fibers of the fiber material to extend without any interruption over each transitional area between the respective end part and the center part of the connecting element. This is because fibers which pass through these areas contribute to these intrinsically critical areas being able to transmit a high power load. Known fiber materials, in particular glass fibers or carbon fibers, may be used as the fibers.
In order to improve the power transmission and to ensure good torque transmission between the flange-like end pieces and the winding former, or the drive-side rotor shaft part, the end pieces are each advantageously provided with an end-face tooth system which engages in a corresponding tooth system of the respective mating piece. The tooth system may intrinsically be designed to be self-locking. Appropriate tooth systems are known per se.
Either metallic low-Tc superconductor material or, in particular, metal-oxide high-Tc superconductor material may be used for the conductors of the superconducting winding. The use of metal-oxide high-Tc superconductor material makes the cooling process easier.